1. Field of the Invention
This invention relates to a device for intensifying pressure of a flowing fluid, and more specifically to a double acting reciprocating intensifier where a single low pressure fluid stream serves as both the power supply and the source of the fluid to be intensified.
2. Description of the Prior Art
Many applications require high pressure fluids at locations remote from high pressure pumping equipment. Pumping fluids to remote locations is commonplace at moderate pressures. However, cost increases dramatically with pressure and remoteness. An alternative approach is to pump moderate pressure to an intensifier which develops the required higher pressure at the site of the application.
Patent disclosures for pressure intensifiers (some of them for downhole and other remote applications) date back a number of years (See U.S. Pat. Nos. 2,293,076, 3,809,502, 3,952,516, 4,047,581, 4,820,136). However, downhole and other remote intensifiers have not come into common use. Other patent disclosures (U.S. Pat. Nos. 3,112,800, 3,901,559, 3,945,207, 4,202,656, 4,458,766, 4,535,429, 4,618,12, 4,705,069) employ the principle of fluid pressure intensification or other relevant principles.
The following examples illustrate specific problems, previous solutions and illustrate the advantages of a remote intensifier. Both problems happen to be downhole. However, other remote applications would benefit similarly from availability of a remote intensifier.
Application 1: DOWNHOLE JETTING
Problem
Petroleum producing and injection wells, and geothermal wells frequently suffer partial plugging from chemical solids that precipitate onto the walls of the well. The extra pressure drop associated with these blockages can significantly affect the efficiency and economics of well operation. Petroleum wells may also suffer accumulations of petroleum solids, such as tars and waxes, that precipitate from the production flow during ascent to the surface. These blockages frequently prevent the passage of tools commonly used in production and workover operations.
Prior Art Solutions
Acids or other solvents are sometimes used to remove downhole deposits. But since there is no practical method for evaluating the completeness of deposit removal during chemical washout, the job may be terminated before removal is complete. Also, small differences in deposit chemistry can cause local variations in the rate of dissolution, thus increasing the risk of incomplete removal. Finally, at least in the petroleum industry, there is a growing reluctance to use chemical solvents because of environmental concerns, and because of the risk of damage to producing formations.
Mechanical methods are also used with varying success. When properly applied, water jets of moderate pressure (2000 to 5000 psi) can remove petroleum deposits and soft chemical scales quickly enough to be economic. However, the rate of removal for hard chemical scales is far too low. To complicate the matter further, the thickness, location and hardness of scale buildup can never be accurately determined in advance. Fine abrasive particles can be suspended in the water to significantly enhance jetting performance. However, abrasive jets also cut metal. The difficulty of accurately controlling the location of a remote jetting tool generally makes the risk of accidental damage to equipment in the vicinity of the jet unacceptable.
Harder chemical scales can be drilled out of well bores with a high degree of success. However, there are several disadvantages to this technique. Only material directly in the path of the drill bit is removed; side pocket mandrels and other irregularities in the internal shape of the well completion are not cleaned out. Also, the drill can cause serious damage to other downhole equipment if it wanders off course. Finally, at the elevated temperatures typically found downhole, positive displacement downhole drilling motors can be expensive to maintain, and have certain fluid compatibility limitations.
A downhole intensifier if available would enhance water jetting performance sufficiently to eliminate the need for abrasives and chemical solvents, and could clean out irregularly shaped areas without damaging metal components at the jetting site.
Application 2: Deep Well Drilling
The rate of progress for rock bit drilling of petroleum and other deep wells can be significantly enhanced when properly assisted by an ultra-high pressure jet (greater than 30,000 psi) of drilling mud or water. The potential economic benefits are substantial.
The only practical prior art method for delivering high pressure fluid to the drill bit is an expensive system comprising high pressure pumps at surface and a drill string with concentric passages for low and high pressure flows. The drill string is specially manufactured at considerable cost premium due to the high pressure seals and manufacturing precision required for leak-tight joints. The concentric passages increase overall pumping energy losses by significantly increasing the surface area of fluid to metal contact. Separate pumping systems are required for the two flows.
A downhole pressure intensifier if available would elevate a fraction of the drilling fluid flow to jetting pressure locally at the drill bit. The balance of flow would circulate normally to transport rock cuttings to the surface. Fluid volume flow rates and pressures could be controlled conventionally. The intensifier would be supplied by a conventional drilling fluid pump and drill string, and its capital cost would be a small fraction of that for the system pumping two pressures from surface.
A prior art reciprocating intensifier uses the pressure energy of one fluid stream to increase the pressure of a second fluid stream via a differential area piston which isolates them physically. Thus disadvantageously, two fluid streams must be supplied to the remote location of the intensifier. Driving fluid in contact with the large piston face compresses and displaces working fluid in contact with the small piston face. On the return stroke of the piston, drive fluid is exhausted and the small cylinder refills with working fluid in preparation for the next power stroke. The process repeats creating an intermittent stream of high pressure discharge. In practice, reciprocating intensifiers generally reduce discharge pressure fluctuation by using two piston sets placed back to back. Under this "double acting" configuration, the combined piston reciprocates as the power stroke alternates from one side to the other. U.S. Pat. No. 2,293,076 describes this process further.